1. A5: Soil Composition
Grade 6

2. Challenge Question
What is the composition of soil? What is it made of?
Mixture of small particles
Rocks, Dirt, and Sand
Water
Air
Organic materials (dead leaves, plants, & animals)

3. Background: Weathered Rock
Soil is different in different places of the world
Soil is a mixture of different things, like rocks.
Rocks become tiny by weathering.
Over time, rocks break by water and wind.
Water may react with chemicals in the rock.
Moving air or water may wear away the rock.
Some rocks fall from higher places and break.

4. Background: Rock Pieces
Scientists named the different size rocks in soil
Sand is the largest piece of rock in soil (~1mm)
Individual pieces (grains) are easy to see.
Silt is 100x smaller than sand (~0.01mm).
Clay is 10x smaller than silt (~0.001mm).
Sand, silt and clay are the main parts of soil.
Different places have different amounts. For example, the desert has a lot of sand in it.

5. Sand Types and Sizes

6. Soil Particle Sizes

7. Sand, Silt, and Clay

8. Sandy Soil vs. Clay Soil

9. Venn Diagram Go to the next blank page in your lab book.
Draw 3 overlapping circles, 2 on top, 1 below.
Label tops “SAND” and “SILT”, bottom “CLAY”.
Write what we just learned about Sand in that circle, but what it shares in the overlaps.
Repeat for Silt and Clay. Write in pencil.

10. Venn Diagram Completed
SAND SILT Big pieces Bigger Medium size Lots of air than clay Rock that’s weathered but not organic Smaller than sand CLAY Smallest pieces Little air

11. Background: Organic Material
Soil has a lot of Decomposed (broken down) material like fruit, plants, animals, and waste.
These are called Organic matter which means material from living things.
Bacteria help break down organic matter.
Eventually it breaks down into basic chemicals called Nutrients, which dissolve in water and are absorbed by plant roots.

12. Questions
Why is it important for plants to grow in soil containing organic matter?
Plants use nutrients from decomposing organic matter to help them grow.
How can a dead plant help another plant live?
Plants remove nutrients from the soil, but when they die they give the nutrients back for the next plant to live. This is called the Cycle of Nutrients.

13. Background: Soil Layers/Topsoil
Soil is made of many layers, each one different
Topsoil is the top soil layer on Earth’s surface.
Its the layer you usually see, about 20cm deep
It is a combination of rock, sand, silt, clay, organic matter, air, and water.
Plants grow roots in this layer, which is rich with biological activity (bugs, bacteria, etc.).

14. Background: Subsoil
Subsoil gets some chemicals from topsoil as water drips and washes nutrients down.
There is not much organic material here.

15. Background: Parent Material
Parent Material is made of broken bedrock.
Plant roots usually do not get down here.
Very little organic matter is found here.

16. Background: Bedrock
Bedrock is hard rock that lies beneath and supports all of the soil layers.

17. Analysis page A23 #2, 3, 6
On a separate paper answer each in 1 paragraph 2) What happens to dead leaves on the ground? 3) Worms help organic matter decompose. In what soil layer do they live? Explain. 6) What is wrong with the school garden soil?